Gripping

ABSTRACT

Use of an object-engaging device in the form of a deformable non-stretch container enclosing a sealed volume of fluent granular material is proposed for at least one of a plurality of force applying members in a gripping apparatus. The container is preferably of a double-walled construction with two flexible walls of which one is elastic, and the inner part is preferably sub-divided. Incorporation of a pressure transducer to indicate applied force conveniently involves the use of electrically conductive granular material to act as a variable resistor.

United States Patent Simpson [451 July 11, 1972 541 GRIPPING [56] References Cited [72] Inventor: David Cumming Simpson, Edinburgh, UNITED STATES PATENTS scmland 3,318,629 5/1967 Brandt ..294/103 [73] Assignee: National Research Development Corpora- 3,509,583 5/1970 Fraioli ..3/ 1.1

tion, London, England Primary Examiner-Even C, Blunk [22] Filed: June4, 1970 App]. No.: 43,539

Foreign Application Priority Data June 13, 1969 Great Britain .,30,169/69 Assistant Examiner-Johnny D. Cherry Attorney-Cushman, Darby and Cushman [57] ABSTRACT Use of an object-engaging device in the form of a deformable non-stretch container enclosing a sealed volume of fluent granular material is proposed for at least one of a plurality of force applying members in a gripping apparatus. The container is preferably of a double-walled construction with two flexible walls of which one is elastic, and the inner part is preferably sub-divided. Incorporation of a pressure transducer to indicate applied force conveniently involves the use of electrically conductive granular material to act as a variable resistor.

3 Clairm, 4 Drawing Figures GRIPPING This invention relates to the gripping of objects and has been developed for use with terminal devices for artificial limbs. However, the invention can also be used in mechanical handling equipment and has a more particular, but not exclusive, application to the handling of irregularly shaped or fragile articles, such as glassware, and to remote manipulation equipment such as employed in radio-active and other hazardous environments.

According to this invention an object-gripping apparatus comprises a plurality of members adapted for application of force therebetween to grip an object, at least one of said members being provided with a deformable object-engaging device in the form of a substantially non-stretch flexible container enclosing a sealed volume of fluent granular material.

In use of such an apparatus, an object to be gripped is normally located between the members and force applied to cause the members to converge towards the object, the arrangement being such that any member having a container as aforesaid engages the object by way of its container. Continued application of this force causes deformation of each engaged container, by flow of the granular material therein, to conform to the shape of the object in the relevant zone of engagement. This deformation is accompanied by a reduction in volume of each container until the granular material packs to effectively act as a rigid body.

Each gripping member concerned can be provided with a container but this is clearly not essential since each container will deform individually under the action of a component of force applied therethrough by its member to the object and other members acting as reaction members. Also, while the above discussion of use assumes involvement of an apparatus acting in the manner of a vice, clamp or claw, say, with powered convergence towards an object to grip the same and divergence away from an object for release, this is not necessarily the case. An outwardly acting gripping action within a hollowed or recessed body is equally possible with the present invention, although the former type of action will be more common as with prior gripping devices.

In any event, it will be apparent that the granular material to be used in application of the invention is selected on the basis of compactability under pressure and fluidity when not under pressure. Sand and talcum are examples of materials which have been found satisfactory in this context during initial development of the invention.

The container in question need not be wholly flexible and indeed will not normally be so by virtue of attachment to its associated member. The container will be flexible at least in a region remote from its member where it is to engage an object.

The container may comprise a single wall, or a number of walls defining inner and outer container parts of which only the former need be sealed. Where inner and outer container parts are employed, the wall of either part, but not both, may be of elastic material whereby the overall container is substantially restored to a predetermined shape when not engaged with an object. This last feature is desirable in practice since the elastic wall will tend to restore the container to a shape having the smallest surface area for its enclosed volume, that is to say it will normally adopt an arcuately curved surface shaping approaching spherical shaping, whereby any deformation under pressure in use will be associated with a reduction in volume. Naturally the elastic wall should not be stressed to the extent hat the enclosed granular material is packed to nonfluency in the absence of other forces.

The outer covering of the container may, whether elastic or not, be preferably chosen to have a high coefficient of friction.

Also, the container may be sub-divided, either by the provision of a plurality of inner containers within a common outer container or by the provision of a plurality of separate containers in close proximity on the same member, to facilitate the flow and redistribution of the enclosed granular material.

Lastly among the more general features of the invention, a pressure transducer may be incorporated in the container to indicate the pressure therein and so indicate initial engagement of the container with an object and/or the degree of force exerted on the object through the container.

In one arrangement for this purpose the granular material itself can serve as part of the transducer by use of material which is at least partly electrically conductive. Then the electrical resistance between suitable electrodes projecting into the container will vary with the degree of compaction, and hence denote pressure.

For a fuller understanding of the present invention, the same will now be described, by way of example, with reference to the accompanying drawings, in which:

FIGS. 1 and 2 diagrammatically illustrate respective views of an embodiment of the invention in released and gripping dispositions relative to an object;

FIG. 3 is a cross-section on the line Il of FIG. 1; and

FIG. 4 diagrammatically illustrates another embodiment of the invention.

Referring to FIG. 1 there is shown an object 1 spaced from and located between two gripping assemblies 2. The gripping assemblies each comprise a container 3, as discussed more generally above, attached to the end of a rigid support member or arm 4.

The more particular construction of the containers 3 in this instance is indicated by FIG. 3. The overall container construction comprises an outer closed container wall 5 of a flexible, non-stretch material affording a relatively high coefficient of friction. Leather is a suitable material for this purpose. Within the outer container are three inner closed container walls 6 of elastic material, the latter being a suitable rubber, say. The inner containers each enclose sealed volumes of a fluent granular material 7 which is electrically conductive. A mixture of talcum powder and carbon granules is suitable for this last purpose. A pair of electrodes 8 project into the central inner container in mutually spaced disposition.

The arms 4 are coupled to respective relatively reciprocable components of a powered mechanism 9, such as a piston-andcylinder assembly or any other suitable means, whereby force can be applied to the arms 4 to cause mutual convergence and divergence-of the container 3.

As described earlier, the containers will tend to adopt an arcuately shaped surface with minimum surface area and maximum enclosed volume by the action of the elastic walls on the powder within the added confines of the non-stretch walls. Indeed, a similar situation will arise even without the use of elastic walls since the powder will tend to adopt an unstressed state throughout its volume when not under pressure by virtue of its fluid-like properties.

In any event, application of force to bring the containers together on to the object causes displacement of powder so that the containers conform to the profile of the object as indicated by FIG. 2. There is an associated reduction in volume of the powder until it compacts to the extent that it acts as a rigid body and so the containers effectively lock in their conformed shapes to grip the object with the applied force substantially evenly distributed over the engaged surface of the object.

Removal of, or reversal of, the applied force to separate the containers from the object causes restoration to the disposition of FIG. 1, the elastic walls serving to enhance the natural tendency for such restoration in the container configuration.

Use of the electrodes 8 within a powder which is at least partly conductive by virtue of the carbon granules provides a pressure transducer facility. Thus, application of a predetermined voltage across the electrodes will give rise to a current signal output variable with the resistance through the powder between the electrodes, this being dependent upon the degree of compaction of the powder, and hence upon the pressure applied to the object. This signal can also clearly be employed to indicate initial engagement with the object by virtue of a signal increase following a substantially uniform signal period.

It is naturally preferable in such a pressure transducer arrangement that the powder be enclosed within electrically insulating material in the form of inner walls, outer wall, or

outer wall and the adjacent portion of the associated force-applying member.

While FIGS. 1 and 2 are employed primarily to give a schematic illustration of the invention, FIG. 4 illustrates an embodiment of the invention more suited to use for an artificial limb terminal device or remote manipulator. In this instance the force applying members are in the form of two fingers coupled at one end for relative pivotal movement to mutually converge or diverge under the action of a suitable powered assembly 11 itself mounted on the end of an arm 12. The fingers 10 are bent or hooked in like manner at their other ends and are provided with containers 13, as discussed above, on their mutually facing portions. The fingers 10 may also be provided with additional containers 14 on their mutually opposed, outwardly facing, free end portions whereby a hollowed object can be gripped by expansion of the fingers within the object hollow.

I claim:

1. An object-gripping apparatus, comprising:

at least two force applying members;

means for moving at least one of said members toward and away from others of said members for engaging and releasing objects;

at least one of said members having a deformable, objecten gaging device thereon, comprising:

a body of fluent material;

a first wall means completely surrounding said body of fluent material, said first wall means including a flexible, elastic portion;

a non-stretch wall means completely surrounding said body of fluent material, said non-stretch wall means including a flexible portion;

the flexible, elastic portion of the first wall means being in extensive surface-to-surface engagement with the flexible portion of the non-stretch wall means to define a composite container, said fluent material normally substantially but loosely filling said composite container, the flexible, elastic portion of the first wall means being so elastic that when the composite container is deformed by engagement with an object, with insufficient force of engagement to compress the body of fluent material to complete non-fluency, the flexible, elastic portion of the first wall means substantially restores the composite container to a predetermined shape having the smallest surface area for the enclosed volume thereof, upon release of the object.

2. The object-gripping apparatus of claim 1 wherein the first 3. An object-gripping apparatus, comprising:

at least two force applying members;

means for moving at least one of said members toward and away from others of said members for engaging and releasing objects;

at least one of said members having a deformable, objectengaging device thereon, comprising:

a body of fluent material;

a flexible, elastic wall means completely surrounding said body of fluent material;

a non-stretch wall means completely surrounding said body of fluent material, said non-stretch wall means including a flexible portion;

the first-mentioned wall means being in extensive surfaceto-surface engagement with the second-mentioned wall means to define a composite container, said fluent material normally substantially but loosely filling said composite container;

the flexible, elastic wall means lying within the non-stretch wall means; wherein the flexible, elastic wall means is composed of electrically insulating material and further includes portions thereof defining compartment walls dividing said body of fluent material into a plurality of mutually segregated portions; at least one of said portions containing electrically conductive articles; and pressure transducer probe means leading from said one portion, through said wall means. 

1. An object-gripping apparatus, comprising: at least two force applying members; means for moving at least one of said members toward and away from others of said members for engaging and releasing objects; at least one of said members having a deformable, object engaging device thereon, comprising: a body of fluent material; a first wall means completely surrounding said body of fluent material, said first wall means including a flexible, elastic portion; a non-stretch wall means completely surrounding said body of fluent material, said non-stretch wall means including a flexible portion; the flexible, elastic portion of the first wall means being in extensive surface-to-surface engagement with the flexible portion of the non-stretch wall means to define a composite container, said fluent material normally substantially but loosely filling said composite container, the flexible, elastic portion of the first wall means being so elastic that when the composite container is deformed by engagement with an object, with insufficient force of engagement to compress the body of fluent material to complete non-fluency, the flexible, elastic portion of the first wall means substantially restores the composite container to a predetermined shape having the smallest surface area for the enclosed volume thereof, upon release of the object.
 2. The object-gripping apparatus of claim 1 wherein the first wall means lies witHin the non-stretch wall means; wherein the first wall means is composed of electrically insulating material and further includes portions thereof defining compartment walls dividing said body of fluent material into a plurality of mutually segregated portions; at least one of said portions containing electrically conductive particles; and pressure transducer probe means leading from said one portion, through said wall means.
 3. An object-gripping apparatus, comprising: at least two force applying members; means for moving at least one of said members toward and away from others of said members for engaging and releasing objects; at least one of said members having a deformable, object engaging device thereon, comprising: a body of fluent material; a flexible, elastic wall means completely surrounding said body of fluent material; a non-stretch wall means completely surrounding said body of fluent material, said non-stretch wall means including a flexible portion; the first-mentioned wall means being in extensive surface-to-surface engagement with the second-mentioned wall means to define a composite container, said fluent material normally substantially but loosely filling said composite container; the flexible, elastic wall means lying within the non-stretch wall means; wherein the flexible, elastic wall means is composed of electrically insulating material and further includes portions thereof defining compartment walls dividing said body of fluent material into a plurality of mutually segregated portions; at least one of said portions containing electrically conductive particles; and pressure transducer probe means leading from said one portion, through said wall means. 